1. Field of the Invention
The present invention relates to semiconductor substrate processing equipment and an apparatus for vaporization and delivery of chemical precursors.
2. Background of the Related Art
Reliably producing sub-half micron and smaller features is one of the key technologies for the next generation of very large scale integration (VLSI) and ultra large scale integration (ULSI) semiconductor devices. However, the shrinking dimensions of interconnects in VLSI and ULSI technology has placed additional demands on processing capabilities. The multilevel interconnect features that lie at the heart of this technology require careful processing of high aspect ratio features, such as vias, lines, contacts, and other interconnects. Reliable formation of these interconnect features is very important to the VLSI and ULSI success and to the continued effort to increase circuit density and quality of individual substrates and die.
As circuit densities increase, the widths of vias, contacts and other features, as well as the dielectric materials between them, decrease to sub-micron dimensions, i.e., 0.5 xcexcm or less, whereas the thickness of the dielectric layers remains substantially constant, with the result that the aspect ratios for the features, i.e., their height divided by width, increases. Many traditional deposition processes have difficulty filling sub-micron structures where the aspect ratio exceed 2:1, and particularly where it exceeds 4:1 or 10:1. Therefore, there is a great amount of ongoing effort being directed at the formation of submicron features having high aspect ratios.
In particular, in order to further reduce the size of devices on integrated circuits, it has become necessary to use conductor materials having low resistivity and materials having low dielectric constants, k, of less than 4.0 to reduce the capacity coupling between adjacent metal lines. For example, one material used to deposit low dielectric constant films is trimethylsilane (TMS). Trimethylsilane is typically deposited by a chemical vapor deposition (CVD) technique or plasma enhanced chemical vapor deposition technique (PECVD) in a processing chamber.
An example of a plasma enhanced deposition of trimethylsilane is described in U.S. Pat. No. 6,287,990, entitled xe2x80x9cCVD Plasma Assisted Low Dielectric Constant Films,xe2x80x9d issued Sep. 11, 2001, and incorporated by reference herein. In a chemical vapor deposition process, trimethylsilane is typically introduced into a processing chamber as a gaseous fluid.
FIG. 1 is a schematic view of one embodiment of a conventional delivery system 10 for delivering precursors, such as trimethylsilane, to a processing chamber 80. The conventional delivery system 10 generally comprises a source of precursor, such as a precursor ampoule 20, operatively coupled (i.e., coupled either directly or indirectly) to a mass flow controller 40, and a processing chamber 80.
Generally, the precursor leaves the precursor ampoule 20 in a gaseous state, and is delivered to the processing chamber 80 via a mass flow controller 40. The precursor moves through the components of delivery system 10 via flow path 25 from the precursor ampoule 20 to the processing chamber 80. The flow path 25 conventionally has an extension into the top portion of the precursor ampoule to minimize liquids from entering the flow path 25. The precursor ampoule 20, the mass flow controller 40, and the processing chamber 80 may be located a substantial distance apart from each other along the flow path 25. Break 90 indicates an abbreviated distance between the precursor ampoule 20 and mass flow controller 40, and the processing chamber 80. The distance between the precursor ampoule 20 and the processing chamber 80 can be 450 feet or more in length.
However, precursors, such as trimethylsilane, in a gaseous or vaporized state may condense or decompose in the lines between the precursor ampoule 20 and the processing chamber 90, and thereby produce an inconsistent precursor flow rate, form a particle problem in the system, or interfere with the deposition of the material in the processing chamber. One solution to prevent condensation and control degradation of the liquid precursors is to heat the lines from the precursor ampoule 20 to the processing chamber 80, such as by a heat trace or by a heating tape, to a temperature above the precursor""s condensation temperature but below the precursor""s degradation temperature. However, heating of the lines, which can reach lengths of 450 feet or more, requires significant installation and operation expense, increased production costs, and increased overall maintenance of the system.
Furthermore, the precursor material, such as trimethylsilane, used in chemical vapor deposition processes are often flammable in a vapor or vaporized state, and require special equipment and procedures for safe handling of the compounds. The additional equipment and procedures also contribute to increased production costs and increased maintenance of the system.
Therefore, it remains a need for a method and apparatus for delivering a vaporized liquid precursor to a processing chamber in a substrate processing system.
The invention generally provides a method and apparatus for vaporizing and delivering liquid precursors to a processing chamber. In one aspect, the invention provides a liquid delivery system, including a liquid supply, a vaporization assembly fluidicly coupled to the liquid supply, the vaporization assembly consisting essentially of an ampoule and a mass flow controller connected to the ampoule, and a processing chamber fluidicly coupled to the vaporization assembly. The liquid precursor is vaporized in the ampoule. In a preferred embodiment, the ampoule is located adjacent the processing chamber to provide point of use vaporization of the liquid precursor.
In another aspect, the invention provides a method for vaporizing a liquid precursor for delivery to a processing chamber, comprising providing a liquid supply containing a liquid precursor, delivering the liquid precursor to an ampoule, vaporizing a portion of the liquid precursor in the ampoule, and flowing vaporized precursor to a processing chamber.
In another aspect, the invention provides a method for vaporizing a liquid precursor for delivery to a processing chamber, comprising providing a liquid supply containing a liquid precursor, heating the liquid supply to a first temperature to provide a first pressure, operating an ampoule at a second pressure lower than the first pressure, flowing the liquid precursor from the liquid supply to the ampoule, vaporizing a portion of the liquid precursor in the ampoule, and flowing vaporized precursor to a processing chamber.